A flock of 18 white birds glided through the cold, blue sky of southern Indiana in the early morning, guided by three small planes disguised as mama and papa birds. Their stop during the 73-day trip from Necedah, Wis., to Dunnellon, Fla., in mid-November was part of an extraordinary effort by Operation Migration to save endangered whooping cranes by establishing a wild flock of migrating birds.